TTI TF830-RS232 Manual De Instrucciones página 4

commands is not allowed except as stated below for CR and LF codes
and XON and XOFF codes.
When an instrument is first powered on it will automatically enter the Non-
Addressable mode. In this mode the instrument is not addressable and
will not respond to any address commands. This allows the instrument
to function as a normal RS232 controllable device. This mode may be
locked by sending the Lock Non-Addressable mode control code 04H
(LNA). The controller and instrument can now freely use all 8 bit codes
and binary blocks but all interface control codes are ignored. To return
to addressable mode the instrument must be powered off.
To enable addressable mode after a instrument has been powered on
the Set Addressable Mode control code, 02h (SAM), must be sent. This
will then enable all instruments connected to the ARC bus to respond to
all interface control codes. To return to Non-Addressable mode the Lock
Non-Addressable mode control code must be sent which will disable
addressable mode until the instruments are powered off.
Before an instrument is sent a command it must be addressed to listen
by sending the Listen Address control code, 12H (LAD), followed by a
single character which has the lower 5 bits corresponding to the unique
address of the required instrument, e.g. the codes A-Z or a-z give the
addresses 1-26 inclusive while @ is address 0 and so on. Once ad-
dressed to listen the instrument will read and act upon any commands
sent until the listen mode is cancelled.
Because of the asynchronous nature of the interface it is necessary for
the controller to be informed that an instrument has accepted the listen
address sequence and is ready to receive commands. The controller
will therefore wait for code 06H (ACK) before sending any commands,
The addressed instrument will provide this ACK. The controller should
time-out and try again if no ACK is received within 5 seconds.
Listen mode will be cancelled by any of the following interface control
codes being received:
12H LAD Listen Address followed by an address not
belonging to this instrument.
14H TAD Talk Address for any instrument.
03H UNA Universal Unaddress control code.
04H LNA Lock Non-Addressable mode control code.
18H UDC Universal Device Clear.
Before a response can be read from an instrument it must be addressed
to talk by sending the Talk Address control code, 14H (TAD) followed by
a single character which has the lower 5 bits corresponding to the unique
address of the required instrument, as for the listen address control code
above. Once addressed to talk the instrument will send the response
message it has available, if any, and then exit the talk addressed state.
Only one response message will be sent each time the instrument is
addressed to talk.
Talk mode will be cancelled by any of the following interface control
codes being received:
12H LAD Listen Address for any instrument.
14H TAD Talk Address followed by an address not be-
longing to this instrument.
03H UNA Universal Unaddress control code.
04H LNA Lock Non-Addressable mode control code.
18H UDC Universal Device Clear.
Talk mode will also be cancelled when the instrument has completed
sending a response message or has nothing to say.
The interface code 0AH (LF) is the Universal Command and response
Terminator (UCT); it must be the last code sent in all commands and will
be the last code sent in all responses.
The interface code 0DH (CR) may be used as required to aid the
formatting of commands; it will be ignored by all instruments. Most
instruments will terminate responses with CR followed by LF.
The interface code 13H (XOFF) may be sent at any time by a listener
(instrument or controller) to suspend the output of a talker. The listener
must send 11H (XON) before the talker will resume sending. This is the
only form of handshake control supported by ARC.
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